This invention relates to an improved non-dripping, heat resistant biodegradable dye penetrant composition and method for non-destructively testing material specimens to locate and identify surface voids, cracks or defects. The invention is especially concerned with a novel dye penetrant composition having the above characteristics, and which can be applied to heated surfaces of an object without decomposition or liquefaction, and without generating fumes, and which in addition has the properties of being readily water washable, and sensitive for disclosing a wide range of defective conditions in parts, employing as solvent or vehicle certain biodegradable nonionic surfactants in the form of certain oxyalkylated alcohols, and mixtures thereof; and to a method of utilizing such dye penetrant composition for non-destructive testing of parts, particularly parts heated to elevated temperature.
In known penetrant inspection methods for rapid location and evaluation of surface flaws or cracks in test bodies or parts, a dye penetrant composition, preferably containing a fluorescent dye, and which will penetrate the openings of the surface cracks or flaws in the part, is applied to the surface of the test body, and the excess penetrant composition is removed from the surface of the body. A developer composition may then be applied to the part surface, which acts as a wick and causes the liquid penetrant containing the fluorescent dye, which was retained in the cracks or surface flaws, to be drawn up out of the surface defects by capillary action. The part is then exposed to appropriate lighting conditions, such as invisible fluorescigenous light, and the location of the surface flaws is revealed by the emission of visible fluorescent light by the penetrant dye which was retained in the cracks or flaws after the penetrant composition was removed from the surface of the part.
For best efficiency, particularly for the detection and location of minute surface cracks and flaws, as well as intermediate size and gross cracks, it is necessary that the dye penetrant composition have high sensitivity.
In addition, stability of the penetrant solution is essential without the necessity for carefully balancing the various liquid components of a dye penetrant solution in order to obtain efficient penetration of the solution into the cracks and flaws of a part, dye solubility, wetting action and washability control.
An additional criterion has recently developed also with respect to dye penetrant solutions and compositions. Generally, dye penetrant solutions presently being used and containing solvents and wetting agents present a disposal problem in that they are substantially non-biodegradable, that is, they are very difficult to decompose by bacteria in sewage disposal plants. Hence the necessity for the development of dye penetrant solutions and compositions which are biodegradable, that is which employ dye solvents and carriers which are biodegradable, and are readily available despite the petrochemical shortage, has attained considerable importance.
In my above U.S. Pat. Nos. 3,915,885 and 3,915,886 there is disclosed novel dye penetrants which have improved washability and sensitivity characteristics, and which are biodegradable, containing as the vehicle for the dye, certain biodegradable nonionic oxyalkylated alcohols.
Further, penetrant inspection of hot surfaces of parts, especially those of overhead and vertical orientation, present a particular problem. Conventional penetrants when employed under these conditions become extremely liquefied, produce obnoxious fumes, drip and change in sensitivity due to loss of volatiles. A conventional dye penetrant employed under these conditions and thinned by the action of heat creates a messy condition because it cannot be contained in prescribed areas of parts or assemblies being inspected.
In my U.S. Pat. No. 3,465,146 there is disclosed a dye penetrant which comprises conventional liquid organic dye carriers or vehicles such as N-methyl-2-pyrrolidone, and a thickening agent such as silica. However, although such composition is effective when applied to surfaces which are at approximately ambient temperature, when applied to heated surfaces, e.g. surfaces heated at temperature in excess of about 100.degree. F., the composition dries and forms a powdery material and fails to perform effectively. In addition, the dye penetrant compositions of this patent are not biodegradable.
Accordingly, an object of the present invention is the provision of a biodegradable heat resistant dye penetrant composition which is a simple formulation and which does not require the use of mixtures of conventional solvents and wetting agents, and which is formed of an essentially single or sole vehicle or carrier for the dye in the form of a biodegradable nonionic surfactant, and which is heat stable, has excellent sensitivity and is essentially non-flammable and non-toxic. A particular object of the invention is to provide a dye penetrant composition of the above noted type, and which incorporates an additive which converts the dye penetrant composition to a gel-like consistency, permitting the dye penetrant composition to be applied to heated surfaces of objects disposed at varying angles, without becoming liquefied and dripping, and without generating obnoxious fumes, substantially without affecting the biodegradability, penetrability or sensitivity of the dye penetrant. A still further object is the provision of procedure employing such novel heat stable biodegradable dye penetrant composition for inspection of cracks, flaws and metallurgical conditions in structural components, particularly parts heated to elevated temperature, without dripping.